2-(1-Hydroxyalkyl)cycloalkanones are useful substances as an intermediate product for synthesis of physiologically active substances or perfume materials. There are conventionally known the methods for producing the 2-(1-hydroxyalkyl)cycloalkanones in which a cycloalkanone and an alkyl aldehyde are subjected to aldol condensation reaction in the presence of water and a base catalyst in a batch mariner (refer to Patent Documents 1 to 3). However, in these batch-type methods, it is required to neutralize the resulting base catalyst aqueous solution with an acid and recover water and residual cycloalkanone contained in an organic layer of the resulting reaction mixture by distillation whenever each reaction has been completed. Thus, the conventional methods are still unsatisfactory in productivity. Also, in Patent Document 3, it is suggested that a water layer formed in an aldol condensation reaction can be reused. However, in this method, in order to reuse the water layer, it is required to once neutralize the resulting reaction mixture by adding an acid thereto and separate the thus neutralized reaction mixture into the water layer and an organic layer to remove the organic layer from the water layer, followed by adding a base catalyst to the thus separated water layer to render the water layer basic. For this reason, in the method described in Patent Document 3, there tends to occur such a problem that the raw materials used for the aldol condensation reaction are deteriorated in solubility in the water layer owing to increased content of the neutralized salt therein, so that the yield of the aimed compound is reduced as the water layer is thus reused repeatedly. Therefore, in the above method, in order to prevent reduction in yield of the aimed compound, the times of reuse of the water layer must be limited, and further a large amount of water which is no longer reusable must be discarded. In addition, the method also tends to have the problem that the cycloalkanone dissolved in the water layer causes a loss thereof.
Patent Document 1: JP-A 56-147740
Patent Document 2: JP-A 2001-335529
Patent Document 3: JP-A 2004-217619